1. Field of the Invention
The present invention relates to a semiconductor electronic part. Examples of the semiconductor electronic part according to the present invention include varistor, PTC thermistor, NTC thermistor, semiconductor capacitor, etc.
2. Description of the Related Art
Various kinds of semiconductor electronic parts are known heretofore. Among these parts, there are known semiconductor electronic parts each having an internal electrode buried in a semiconductor ceramic substrate.
The semiconductor electronic part of this type obtains semiconductor characteristic by utilizing contact between the internal electrode and the semiconductor ceramic substrate. The semiconductor ceramic substrate is selected in accordance with the kind of the semiconductor electronic part to be obtained. A material for constituting the internal electrode is selected so that predetermined semiconductor characteristic is obtained between the semiconductor ceramic substrate and the internal electrode.
As described above, in the semiconductor electronic part of this type, the composition of the internal electrode is required to be selected so that predetermined semiconductor characteristic can be obtained in accordance with the semiconductor ceramic substrate. In the case of a capacitor, or the like, strength of adhesion can be improved by adding a third component such as glass frit or the like to the constituent material for the electrode. However, if such a means is applied to the semiconductor electronic part, the semiconductor characteristic deteriorates. Hence, the semiconductor electronic part basically has a problem that it is difficult to improve strength of adhesion of the internal electrode to the semiconductor ceramic substrate.
For example, in the case of a varistor, a titanium oxide type substrate, a strontium titanate type substrate or a zinc oxide type substrate is generally used as the semiconductor ceramic substrate. Such a semiconductor ceramic substrate per se has voltage nonlinearity. In order to extract the voltage nonlinearity of the semiconductor ceramic substrate, the internal electrode must be selected from materials which come into ohmic contact with the semiconductor ceramic substrate. Specifically, the internal electrode must contain silver as a main component and at least one member selected from the group consisting of In, Ga, Sn, Sb, Cd, Zn and Al as an additive component. If glass frit, or the like, is added to improve strength of adhesion, ohmic contact characteristic deteriorates and, accordingly, voltage nonlinearity deteriorates.
As described above, in such a semiconductor electronic part, strength of adhesion between the internal electrode and the semiconductor ceramic substrate was generally insufficient, so that various troubles occurred in production steps. Actually, in the steps of producing the semiconductor electronic part, there are several steps for acting physical stress such as thermal contact bonding, cutting, separation, etc., on the semiconductor ceramic substrate. Hence, there was a risk that the physical stress might cause troubles such as electrode peeling etc. at an end edge of the semiconductor ceramic substrate. As a result, failure in characteristic occurred frequently. This caused lowering of the yield of products.
An electrode shaped like an I-type pattern or a T-type pattern is generally known as the internal electrode in the semiconductor electronic part.
If the internal electrode is shaped like the I-type pattern, the aforementioned problem appears more remarkably. Specifically, if the internal electrode is shaped like the I-type pattern, the internal electrode has a small portion exposed at the end edge of the semiconductor ceramic substrate. Hence, when a terminal electrode was applied onto the semiconductor ceramic substrate and baked, strength of adhesion between the internal electrode and the terminal electrode was so weak that failure in characteristic occurred in the peeling test (easy adhesive strength test).
If the internal electrode is shaped like the T-type pattern, the internal electrode has a large portion exposed at the end edge of the semiconductor ceramic substrate in comparison with the I-type internal electrode. Hence, strength of adhesion between the T-type internal electrode and the terminal electrode is larger than that between the I-type internal electrode and the terminal electrode so that the occurrence of electrode peeling decreases. In this case, however, chopping or cracking was easily caused by physical stress because the internal electrode is exposed up to a corner of the semiconductor ceramic substrate. As a result, failure in characteristic occurred frequently. This caused lowering of the yield of products.
An object of the present invention is to provide a semiconductor electronic part in which strength of adhesion of an internal electrode to a semiconductor ceramic substrate is so large that troubles such as electrode peeling, chipping, cracking, etc. can be prevented securely.
Another object of the present invention is to provide a semiconductor electronic part which is high in reliability because failure in characteristic little occurs.
To solve the aforementioned problem, the semiconductor electronic part according to the present invention comprises a semiconductor ceramic substrate, and at least one internal electrode.
The internal electrode is provided inside the semiconductor ceramic substrate. The internal electrode has one end side led out to an end edge of the semiconductor ceramic substrate, and at least one cutout region. The cutout region is provided inside the internal electrode.
As described above, the internal electrode is protected by the semiconductor ceramic substrate because it is provided inside the semiconductor ceramic substrate. Hence, a semiconductor electronic part excellent in corrosion resistance, oxidation resistance, impact resistance, etc. is obtained.
The internal electrode has one end side led out to an end edge of the semiconductor ceramic substrate. According to this structure, the semiconductor electronic part can be used as a chip-like electronic part by adding terminal electrodes to end edges of the semiconductor ceramic substrate.
The internal electrode has at least one cutout region at its one end side. According to this structure, the cutout region of the internal electrode is filled with the semiconductor ceramic substrate as if the internal electrode is stitched by the semiconductor ceramic substrate filled in the cutout region. Accordingly, strength of adhesion between the internal electrode and the semiconductor ceramic substrate increases. Hence, troubles such as electrode peeling, chipping, cracking, etc. can be prevented securely. As a result, a semiconductor electronic part which is so high in reliability that the occurrence of failure in characteristic can be reduced is obtained.
Preferably, a plurality of cutout regions are provided. In this case, strength of adhesion between the internal electrode and the semiconductor ceramic substrate can be increased more greatly compared with the case where one cutout region is provided. Hence, troubles such as electrode peeling etc. can be prevented securely. As a result, the reliability of the semiconductor electronic part is improved more greatly, so that the occurrence of failure in characteristic is reduced more greatly.
Preferably, the cutout regions are provided to be distanced from one another in a direction of the width of the semiconductor ceramic substrate. In this case, strength of adhesion between the internal electrode and the semiconductor ceramic substrate can be increased more greatly compared with the case where one cutout region is provided at one side of the internal electrode in the direction of the width thereof. Hence, troubles such as electrode peeling etc. can be prevented securely. As a result, the reliability of the semiconductor electronic part is improved more greatly, so that the occurrence of failure in characteristic is reduced more greatly.